Ordinary hand-held two-stroke engines can work in any working posture, such as a tilted or laterally overturned posture, without limitation from lubrication structures. Currently, regulations on pollutant emission in China are becoming stricter. Therefore, the above two-stroke engine is not suitable any more as its exhaust contains lots of pollutants.
However, although ordinary four-stroke engines are better than the two-stroke engines in exhaust emission, existing lubrication systems cannot meet the requirements of the four-stroke engines. If the four-stroke engine turns over or rolls over, the running of the lubrication system becomes poor, or even worse, it will cause the engine to burn or leak lubricating oil.